This invention relates to the treatment of silicate based hollow microspheres to improve their stability in aqueous environments. The invention comprises treating said microspheres with multivalent metal ions, thereby modifying the surface of the microspheres.
Hollow microspheres such as those described in U.S. Pat. Nos. 3,796,777; 3,794,503 and 3,888,957 are formed by spray drying alkali metal silicate solutions that have been combined with "polysalt" solutions. While these products are satisfactory for use in essentially non-aqueous environments, they are sufficiently sensitive to water to prevent their universal acceptance in aqueous systems.
Fused glasses, used in bottles and similar items, have been treated with multivalent metal ions to improve weathering qualities of the product. Such treatment consists of the vapor phase reaction of a compound such as aluminum chloride with the glass as it is cooling from fabricating temperatures of up to 1000.degree. C. During this time, glass is considered to be in its most reactive state. U.S. Pat. No. 3,337,321 and Swedish Pat. No. 10372/1955 (issued May 4, 1961) illustrate such processes.